1. Field of the Invention
The present invention relates to a machine tool capable of diagnosing the abnormality of a speed reducer used in a tool changer thereof having a tool magazine.
2. Description of the Related Art
As a method for diagnosing the abnormality of a speed reducer, there has been known a method in which a sensor is installed at a diagnosis target part and the abnormality of the speed reducer is diagnosed based on information from the sensor. According to this method, detection of an abnormality is made after the abnormality occurred, so abnormality prediction is not possible. Further, as a method for predicting abnormality, there has been known a method in which a vibration pattern is detected by a vibration sensor and the vibration pattern is compared with a normal vibration pattern to predict the abnormality in advance (see Japanese Patent Application Laid-open No. H5-52712). However, since noise is contained in a signal from the sensor, the method cannot clearly distinguish between normality and abnormality.
Furthermore, as a method and an apparatus for predicting the abnormality of a speed reducer, there have been known a speed reducer abnormality diagnosis method and a diagnosis apparatus in which disturbance torque is estimated by an observer based on the torque command and the speed feedback of a motor, time-series data on the estimated disturbance torque is subjected to frequency analysis in order to extract a specific spectrum corresponding to a constant multiple of the rotational frequency of the intermediate element of the speed reducer, and abnormality is determined when the amplitude of the specific spectrum exceeds a threshold (see Japanese Patent Application Laid-open No. 2008-32477). In the method, with no noise being contained in data, the abnormality of the speed reducer can be accurately diagnosed.
With the above speed reducer abnormality diagnosis method in which disturbance torque is estimated by the observer and the abnormality of the speed reducer is detected based on the estimated disturbance torque, it is possible to accurately predict the abnormality of the speed reducer. However, in a case in which the method is applied to a speed reducer used to rotate a tool magazine in the tool changer of a machine tool, inertia on the output side of the speed reducer changes, which results in a change in disturbance torque when tools are replaced. Therefore, the method has a problem with accurately diagnosing the speed reducer when the tools are replaced.